title: Differential impact of a complex environment on positive affect in an animal model of individual differences in emotionality.
abstract: Anhedonia, or the inability to experience positive feelings is a hallmark of depression. However, few animal models have relied on decreased positive affect as an index of susceptibility to depression. Rats emit frequency-modulated ultrasonic vocalizations (USVs), designated as "positive" calls in the 50-kHz range. USVs have been associated with pharmacological activation of motivational reward circuits. Here we utilized selectively-bred rats differing in "emotionality" to ask whether there are associated differences in USVs. Rats bred based on locomotor response to novelty and classified as bred High Responders (bHRs) or bred Low Responders (bLRs) exhibit inborn differences in response to environmental cues, stress responsiveness, and depression-like behavior. These animals also exhibit differences in anxiety-like behavior, which are reversed by exposure to environmental complexity (EC). Finally, these animals exhibit unique profiles of responsiveness to rewarding stimuli accompanied with distinct patterns of dopamine regulation. We investigated whether acute and chronic environmental manipulations impacted USVs in bHRs and bLRs. We found that, relative to bLRs, bHRs emitted significantly more 50-kHz USVs. However, if a bLR is accompanied by another bLR, there is a significant increase in 50-kHZ USVs emitted by this phenotype. bHRs emitted increases in 50-kHZ UVSs upon first exposure to EC, whereas bLRs showed a similar increase only after repeated exposure. bLRs' increase in positive affect after chronic EC was coupled with significant positive correlations between corticosterone levels and c-fos mRNA in the accumbens. Conversely, a decline in the rate of positive calls in bHRs after chronic EC was associated with a negative correlation between corticosterone and accumbens c-fos mRNA. These studies demonstrate that inborn differences in emotionality interact with the environment to influence positive affect and underscore the potential interaction between glucocorticoids and the mesolimbic reward circuitry in modulating 50-kHz calls.
authors.affiliation: Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA 23219-1534, United States. Electronic address: perezja12@gmail.com.
authors.forename: J A
authors.initials: JA
authors.lastname: Perez-Sepulveda
authors.affiliation: Department of Psychiatry, University of Michigan, Ann Arbor, MI 48109, United States; Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States; Department of Psychology, University of Michigan, Ann Arbor, MI 48109, United States.
authors.forename: S B
authors.initials: SB
authors.lastname: Flagel
authors.affiliation: University Research Institute on Health Sciences, University of the Balearic Islands, Palma de Mallorca, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: Garcia-Fuster
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States.
authors.forename: R J
authors.initials: RJ
authors.lastname: Slusky
authors.affiliation: Department of Psychology, University of Michigan, Ann Arbor, MI 48109, United States.
authors.forename: J W
authors.initials: JW
authors.lastname: Aldridge
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States.
authors.forename: S
authors.initials: S
authors.lastname: Watson
authors.affiliation: Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States.
authors.forename: H
authors.initials: H
authors.lastname: Akil
mesh_terms: D000339:Affect; D000818:Animals; D001007:Anxiety / Q000523:psychology; D001522:Behavior, Animal; D003345:Corticosterone / Q000378:metabolism; D003863:Depression / Q000378:metabolism / Q000523:psychology*; D004195:Disease Models, Animal; D004777:Environment; D005106:Exploratory Behavior; D016762:Genes, fos / Q000235:genetics; D007206:Individuality; D008124:Locomotion; D008297:Male; D009714:Nucleus Accumbens / Q000378:metabolism; D012333:RNA, Messenger; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D013315:Stress, Psychological / Q000378:metabolism* / Q000523:psychology; D014465:Ultrasonics
chemical_list: D012333:RNA, Messenger; D003345:Corticosterone
keywords: affect; emotionality; individual differences; ultrasonic vocalization